Having been pregnant, i can guarantee the last thing on my mind was jumping. for the first 3 months or so i felt sick, then i suffered from indigestion, then i spent the last few months feeling fat and out of sorts.
Personally, i'd get her checked over by a vet if you are concerned with her change in behaviour, and if you are going to work her, then make sure it is light work. something like trail riding or similar.
Ive had one mare that was ridden until a couple of weeks before her bub was due, and i've also had others that didn't want a bar of a person from about a month from the service date.
so yeah, in your situation, i'd probably get a vet check to start off with.
My Number 1 Rule When Owning A Horse:
"HANG OUT WITH THEM AND BE THEIR BUDDY, THEN THEY'RE YOURS FOR LIFE"