Geez, we had this situation with our boys' team this year. For the first meet, the experienced parents organized a borrowing brigade, and because we couldn't muster enough tiny singlets, we got them super cute matching teeshirts with the gym's logo on them (allowed at L4). It should not be that hard to find one person with a leo and warmups your daughter can borrow! The person in charge of managing uniforms should have been on this a few weeks ago.
If you have practice today, can you ask around at pickup to see if someone in an earlier or later session has a leo your daughter can borrow? The only alternative would be to go with MILgymFAM's suggestion.
This is stressful, I know, and I'm frustrated on your behalf, but in the grand scheme of things, don't worry too much. It's not the end of the world if she's not a perfect match with her teammates at the first meet, and the gear will eventually arrive. If your team has parents managing comp gear, I bet I know who's going to be helping out next year . . .