The dilemma: My boyfriend is 52 and I am 38. We have been together a year-and-a-half and are trying for a baby. The big cloud on our horizon is his youngest daughter, who is 22. Although my boyfriend separated from this girl's mother 'officially' two years ago (and I was not the cause), she has decided we are her enemies. She has just moved back to our city after three years away, and has made us absolutely miserable. She lives with her mum, who still pines for her ex, and she only listens to her mum's side of things. She ignores me on the street, comes over at seven in the morning to berate her dad, sends him horrible accusatory emails and has ganged up with her mother to sue him for 'child support', so he has to pay all her costs while she goes to university. She is jealous of me, and tells her dad he's in an 'abusive relationship', but the abusive behaviour is from her side, not mine. I've done nothing but try to make her feel welcome in our house. I know this kid is in a lot of pain, but I am furious about how she treats her dad. If we have a baby, she won't want to come near us and will treat us all like her enemies. How can I get over this?

Seems to me the question is: how can she get over this? You've accepted her challenge and made it a personal tussle between the two of you. That's a mistake. Reading your letter, this girl sounds like a monster, which always makes me suspicious. And excuse my ignorance, but I'm pretty sure you can't sue for child support for an adult over 19. That said, they may well be trying to make her fees part of the divorce settlement, but that seems fair enough, and surely something that he doesn't resent?

I've got a hunch that you are exaggerating the level of hysteria and therefore playing a part in raising the level of this high-voltage conflict. If, as you say, when you have a baby of your own together she will 'not want to come near you and treat you all like enemies', won't it be the answer to your prayers? If you can't make her love you, you can at least hope she learns to ignore you. Or do you find that a problem? You say she ignores you on the street, which - if the alternative is histrionics - should surely also be a relief? On the one hand you are criticising her for turning up on your doorstep at unreasonable times and making your lives miserable, on the other you are fretting that she might cut you off. Spot the contradiction.

There's little mention in your email of your partner's reaction to all of this. Clearly his daughter is upset at her parents' split. To you, two years of 'official' separation may seem like forever, but to his daughter the wound is still pretty raw. It's not easy to move sanguinely from divorce to embracing a third party. Maybe you need to be a little more understanding of those he's left behind. It's a phase that will pass as her own life gets busier and more complicated, but for now, if you rise to her challenge you'll be contributing to your own misery on a major scale.

As you'll learn when you have your baby, toddler tantrums are best ignored. It's also the case when overgrown babies start stamping their feet. The more dignified and placid you can be under attack, the less attractive a target you'll seem for this fiery young madam. Try, conversely, to imagine how delighted you'd be if your future child were to grow up displaying the same protective ferocity toward you. It would be quite flattering, I imagine!

I'm not saying that this is a sustainable situation. Nevertheless it is one that you will have to endure for a little bit longer. Employ your emotional energy in patching up your boyfriend's scars from the divorce proceedings and making that baby, rather than rolling up your sleeves and going for his daughter. Divorce is a painful business, which is why I'm surprised so many people embrace it as the first option in a difficult marriage rather than their last. It's often not until you're out the door that the true scale of the damage begins to emerge. I can't help feeling that whatever you are dealing with now has little to do with you and an awful lot to do with past history. While I'm sure your partner is nothing but honest with you about his marriage, you have to remember that his is a wholly subjective viewpoint. There's bound to be plenty of unexplored resentments that he's not even aware of.

So tread softly over his past and concentrate your energy on your future together. His daughter will come round to your relationship in time, and that moment will arrive so much sooner if you give her some space now to let off steam. It's not your fight, so keep your fists down.

If you have a dilemma, send a brief email to mariella.frostrup@observer.co.uk