AITH or is this just selfish behaviour ?

I’m feeling a little frustrated and quite frankly angry. I have a friend who is a single mom, she doesn’t have much family here and only a few friends. I try to help her out when I can with her kids but I have kids of my own too. She frequently asks me for help and I feel backed into a corner because she doesn’t really always ask for help so much as say I need to help her. At the beginning of the year her and her boyfriend had a big blow up and they almost broke up. She asked me to watch her kids so she could work, letting me know that she desperately needs the money. So my husband and I agreed and spent two of his days off (he had taken vacation way before this) to watch her kids. Her kids were sick and she played it off like no big deal. Fast forward a couple days later and my husband and youngest were really sick. My youngest ended up needing antibiotics and I also ended up really sick and needed to call into work. A couple weeks later I announced my pregnancy to her.

This past week she called and said her boyfriend was experiencing a medical emergency and she needed to take him to the hospital. She asked if I could watch her kids and said they were sick again. I hesitated but she said I was her only option as her ex (the kids dad) would use this as fuel in his battle for more custody of the kids. She dropped them off, and left and a few hours later her youngest started throwing up from how bad her cough was. Didn’t take long and now my family is sick again, and I’ve been laid up in bed going on three days. I’m still early in pregnancy, this is rainbow baby after a miscarriage, and I’m so worried about this somehow affecting the baby. Not to mention I likely will have to call into work again this week because of this. My husband works from home, thankfully, but he’s been pulling double duty caring for the kids and working which means long days for him because I’m physically so sick (not to mention morning sickness).

I don’t know what to do about it and while I want to be a good friend and help when I can, I feel like she’s been selfish and makes me feel guilty if I can’t watch her kids. I’m not a germaphobe or anything, but I do feel really taken advantage of.