Hi Margaret! I can totally weigh in here, as I remember when we first had the opportunity to do Steeplechase and Grand Prix.
There are a couple things to consider.
1. What are your USDAA goals with Phebe? Do you plan to continue w/USDAA? Do you want to compete in Nationals eventually? Would you like her to get her ADCH?
2. Do you have the money to spare? Tournament qualifiers are usually more expensive ($20+)
The tournament qualifiers, in my opinion, serve one of three purposes.
a) To get experience. BUT, consider that they are usually the most expensive runs.
b) To qualify for Nationals (the qualification only is for the year in which you earn it)
c) To count towards your dog's ADCH. The dog needs 10 Tournament Qualifiers, and at least 1 in each event (Team, Steeplechase, and Grand Prix)
I was told to go ahead and enter Steeplechase because it is run by (sort of) Starters rules. So, you can make a mistake (drop a bar, pop the weaves--if you fix it) as long as Phebe is under time. It is time + faults (a fault is a 5 second addition to her time). Also, since it is time based, if you do want Phebe to get her ADCH, it is best to do Steeplechase while she is young and fast. Steeplechase is about speed, not technicality.
Grand Prix, on the other hand, is run by Masters rules. So refusals (hesitations) and all faults are an automatic NQ. I find that these courses are typically much more technically difficult.
When we first were trialing, we did Steeplechase and not Grand Prix. But it's sort of up to you and your goals.
Hope that helps!