oh dear oh dear - she's certainly letting the side down by banging on about it.
First of all, being a single parent is hard - effing effing hard if the truth be told. it's the relentlessness of it, that everything is down to you, you have no-one to bounce your parenting off (let alone getting some personal needs met, perfunctory or otherwise). I do think that people who are in relationships can have no idea what it is really like tbh, though people certainly do try to imagine what it could be like - the better people anyway.
You're one of them OP (you darling woman!). BUT it looks like she's having a good old pity party about it all and, horror, constantly bleating about her lot. That won't do. If someone with no legs constantly says 'it's alright for you, you've got two legs' as though the universe hangs on it, well, that just won't do and is bad form.
I don't think I've ever used the phrase tbh, though i have been a SP for donkey's years - I know i don't use it much because when people do use phrases a lot they end up swallowing most of the phrase (think politicians) it is so well worn, like a stair carpet - and I don't do that. I just got on with it , it's been hard enough without drawing attention to it.
You are mrs lovely and you are bending over backwards to accommodate your friend's needs - tbh, you're wasted on her: there are plenty of SPs who would be overjoyed to find someone like you as a good friend who doesn't put her marriage/man on a pedestal before which the world has to STOP (rare) - uh-oh, sounding bitter there.
She's got to shut up, plant her feet firmly like the queen, and bear the load. Of course some marriages are shit and it's horses for courses: that doesn't take away how hard it is to be a SP, sorry - a different kind of hard, admittedly. It does get on my nerves when people say they would love to be able to do what they like when they like, aren't you lucky - try that year in year out and it does lose its gloss.
Tell me, why are you flogging a dead horse OP? Does she have any redeeming traits? Does she give anything to you? You have obviously established a forum where she feels it's ok to bleat constantly - why is that? Is she your lame duck (sorry, blunt), are you a helper? Just a thought.