Should I break up with my 'friend'?

I think I need help breaking up with a 'friend'.
There is a woman who I know through school. We have been on friendly terms for three years now as our children have been in the same class together. I have helped her out at various school things, as she has helped me, but I have been resistant of becoming friends as she has different standards and morals to me when it come to raising children. Some of her stories about her children and what they get up to are quite horrifying and just in really bad taste. I am a pretty laid back parent but things like taking photos of your children doing brown-eyes really just isn't my thing.
Anyway, I have found her to be incredibly needy lately and it seems like every time I see her she is asking me to do something. Whether it be dropping her kids home from school (a 40 minute round trip when I live 5 minutes from the school), to babysitting her children on weekends, having them for sleep overs, using our pool, doing shopping for her... It is just never ending with three or four large favours asked every week. I think she is just lazy and doesn't want to do these things herself. I don't like her kids coming over as her son (9 yrs) has been overly sexual with my girls - kissing them on the thighs and pulling down their knickers - and I just don't trust him to be around them - especially not for a sleepover!!. Her husband has just been diagnosed with a life threatening illness so the requests of favours and help have increased 10 fold and I'm finding it hard to believe someone closer to her can help her rather than me! I'm not comfortable with this family but feel like this is terribly bad timing in light of the husbands illness and trying to ease away from her may be construed as abandoning her in her time of need. But honestly! Is this normal behaviour or is she toxic and I just need to get the hell out of this 'friendship'??? Hit me with your advice please!