need help - looking for one specific movie/cartoon

Hello there folks!

my gf is a total Betty-addict but there is one thing she/we can't figure out:

She keeps telling me, that the first thing she remembers of Betty, is a movie/cartoon she watched when she was a kid (like 6 years old). The videotape got lost over the years and all she remembers (or at least she thinks she remembers - its all pretty blurry) is the following:

- she claims it wasn't a short movie, it was a proper videotape (maybe we can ignore that - it might have been a tape with many shorter cartoons in a row).
- she remembers there were centaurs involved
- she remembers there was someone playing polo
- it was in a way scary (like themes and music)
- betty was driving or driven in a black car

Obviously we cross-checked the internet and watched "all" the available cartoons on youtube (source was the english wiki page - it lists all cartoons at the bottom (I just registered for the forum so i can't post the link )).

So I really need your help - it would make her unbelievably happy to find out what she saw as a kid. Any ideas are much appreciated!