Jealousy

Hi guys. I’m sure some of you have been in this situation and I’m wondering how you handle it. I have a 2 year old and a 7 year old stepdaughter. When it comes to birthdays and holidays (Christmas, Easter) we spend the same amounts on both of them. My stepdaughter is here 50% of the time. There are times when the youngest will get things when the oldest is with her Mom. (Nothing major maybe a $5.00 toy or book) the second the oldest gets here she starts looking around to see what my youngest got while she wasn’t here. I try to explain to her that she gets stuff from her Mom when she’s there so sometimes the youngest gets stuff when she’s not here. It’s getting so frustrating I don’t know how to handle it. We don’t have a lot of money so I can’t buy for both all of the time but I feel if I have my daughter out somewhere I should be able to get her a little something and not feel guilty about it. If both kids are here I obviously get something for both. Anyone been in this situation? How did you handle it?