Definition: Given a real-life anecdote of a complex ethical situation, generate a suitable title that describes the main event/root cause of the situation. Imagine that the given text is a social media post, and you have to write the title of the post, so the users can decide to read the main text or not.
Input: Okay so from the title alone, I definitely sound like the asshole. But hear me out. 

I'm a nanny for two lovely kids. I love them, but the family pays me a laughably small amount of money for the work I put in. I work about 8 hours, four days a week for 150 a week. 
This is my second job, I also work a more "career" part time job in the evenings. I took the nanny job not for the money but because it's something I enjoy doing while I'm not working at my "real" job. 
However, the parents can be... demanding. Often, they will ask me to come early or on days off without paying me extra. I can be a bit of a pushover, so I usually make their requests work if I can. Well, the mom is pregnant with her third child it's made things more difficult for me, but I wont get too into that. 
The case in question: She has an ultrasound appointment in a few weeks to find out the gender. Last time she had an appointment, she called me (on my day off) at 8 am as they were on their way to the doctor to ask if I could watch their kids. Due to the way my two work schedules lined up, this was my only day off that week. I tried to tell her that, but she said stuff along the lines of "I know, and I will be so appreciative for your help. You dont understand how hard it is to have kids at a dr. Appt," etc, etc, basically cornering me and giving me no choice. Finally, I caved and agreed to meet her to take the kids. 

Fast forward, last week she posted online that she has an ultrasound appointment in couple weeks to see the gender. I immediately know exactly what is going to happen, shes going to call me (at best) the day before to ask me (tell me) to watch her kids so she and her husband can go without them. My first instinct was to just plan for this and keep my schedule clear that day. Then the asshole(?) in me remembered that my boyfriend and I had been planning a mini vacation next month. I asked him if he would be okay with doing it early, and we ended up working it out so we will be going on our long weekend trip at the same time as this doctors appointment. I thought this way, when she calls at the last minute, I will have a firm excuse for why I cant help, and she will have to figure something else out  

Then I started to feel like an asshole. I feel petty for going out of my way just to get out of helping someone, especially cause I know they dont have anyone else around to help them. I feel spineless for not being able to just stand up for myself and say no. Then again, this is a vacation we were going to take anyway, they dont pay me extra to help on these extra days (cause they pay me by the week), and she has a really skillful way of manipulating people so it's just impossible to say no to her sometimes. 

The vacation is planned and the hotel is booked so I cant take it back, but I'm wondering how guilty I should feel about this. AITA? 

planning a vacation when I know I'll be asked to work