[US] Is my nail artist friend getting scammed?

My friend is a nail artist and she does amazing nails for a relatively good price ($50). She told me that there is a party of 6 who want her to do their nails which would be $300. She asked the lady how they’re gonna pay if it’s gonna be separate or together and the lady said “we are gonna pay altogether, one check.” My friend says she only takes apple pay, cash app, venmo, etc. and the lady insisted on a “mobile check” for the party planner. Anyways my friend was okay with that, but then the lady said she’s gonna need my friend to pay the partygoers’ bus driver because the planner/organizer only does “mobile checks” while the bus driver takes cash. My friend asked how much she needs to pay, and the lady says $600! So my friend is about to get a $900 payment, with only $300 of that money actually being hers. I’m 99% sure this is a scam but can someone let me know so I can save my friend from potentially being out of a couple hundred dollars?