:( :( so much myth, so much misunderstanding, so much contradictory stuff :( :(
MPD - you said this is what you have been told.
"Don't let her feed for longer than 30 mins at a time, lest the feeding in itself becomes too tiring"
A healthy, term baby - which yours is - does not need to have feed times limited in this way - this might be appropriate for a sick, weak, vulnerable pre-term and even then they can be cared for with 'kangaroo care' - you just would not be struggling to feed them for lonf.
"only feed from one side (for up to an hour) to allow the other to fill up adequately ("
NO!!!!!! Anyone who says this does not understand how breasts work - anything they say can be ignored. For an explanation of why this is totally wrong, see www.kellymom.com (BullyBeefBadgers you were misled - great you got things sorted, but it was everything else you did that helped, not that :( ) This idea that babies need to drill down to the fattier milk is responsible for a lot of confusion; it is volume of milk that drives weight gain, and the foremilk/hindmilk sorts itself out with no engineering...in the majority of cases.
"and only allow the feeding/expressing/topping up bit of the three hours to take about an hour so that there is time to rest (for me) in between feed times."
That has a grain of common sense - not to make a great long performance of feeding/expressing/topping up, to give you a break, but it's really prescriptive to say an hour. The main thing would be to avoid that treadmill of feeding/expressing/topping up, if possible, in favour of direct breastfeeding.
Hope today goes better, MPD.