Is This Pony Pregnant?

When I bought Rosie Pony back in October (?), I was warned that there was a chance she was pregnant. She had "had access" to a stallion, but no-one had actually witnessed any breeding. Well, she's been getting fatter and fatter since she came to stay with us, and several horsey-type people who have seen her have said she is either severely overweight or pregnant. Or both, I suppose that's a possibility. What she could possibly be getting fat ON is a mystery to me, since all I give her is the same hay I feed the goats, which isn't really very good hay, and a handful of alfalfa pellets morning and evening. 

I kind of hope she's pregnant.