Hi there and welcome to the boards!
You could try a 3.5 hour EASY (are you familiar with EASY - have you read Tracy's books?), formula fed babies do need to go longer between feeds earlier than breastfed babies. I think she is a bit little for 4 hours, as she won't be able to do the 2 hours A time needed for a 4 hour EASY.
The feeds she takes now sound very normal to me and the nightfeed is totally normal for a while yet, the fact she wakes at different times does indicate hunger rather than habit.
I also wouldn't worry too much about what your HV says, follow your instincts! Babies gain weight at different rates and will gain more some months than others - I bet if she gained a lb in a week being breastfed they wouldn't be suggesting less milk
!
If you post your day for us we can have a look and see if any tweaks will help overall, so
Eat - what times, how much
Activity - how long for
Sleep - what times, how long for
HTH!
Laura