43 Minute Connection in DEN - Enough Time?

I’m trying to book a flight from STL to SEA for my sister and she needs the last flight to get work done that day. What I’ve found is:

UA 7876 (United Express) Depart: STL 06:54 PM: Arrive: DEN 08:12 PM
UA 509 Depart: DEN 08:55 PM: Arrive: SEA 10:39 PM

But that 43 min connection has me worried.

Does anyone know if the gates will be close together? Or because its United Express will they be at opposite ends of the terminal?

Should she just give up and catch an early flight the next morning?

Thanks for any advice,

Rich