Trying to avoid drama- EDITED

Okay, so I hate confrontation... it makes me so uncomfortable and I’ll avoid it at any cost. I don’t know what to do or say in this situation, help!

For the past 3 months I’ve been helping a friend out by watching her kids when she needs it, and in return she would trade me professional photos of my family/kids. Here’s my dilemma- she claims to have been keeping track of the hours I worked, but when I go back and look at my own personal log the amount of hours doesn’t add up to what she says. I’ve spent about 10 hours ($100 value) more than what she says I’ve done.

She’s hosting a photography event that I assumed my kids would get to participate in as I’ve made up for the cost of it with babysitting hours, but she just sent me an invoice to pay for it. I really want these photos, so I’ll pay for it of course but I’m kind of frustrated about it.

***edited to add: I don’t think her intentions are malicious, I hownstly just think that she’s an busy mom who may not have kept track as well as she could have.**