- how come River can't remember killing Doctor in spacesuit - and wouldn't the later River have tried to stop it at the time
Well we don't know what exactly was in the space suit, there may be a twist here. River does say in a previous episode that it isn't her death that she is worried about, that there is a far worse day coming for her. Perhaps it is River as an adult and thus this a future version of herself.
- how come she didn't seem to remember being in the spacesuit or was she just being a really good actor
ditto
- if the reason she's imprisoned is that she killed the Doctor, how come in the story on the weeping angels she's helping out the monks (who helped create Melody the assassin in the first place to kill the doctor) and therefore earns a pardon - because presumably those who imprisoned her didn't agree with killing the doctor IYSWIM
Not sure I follow this, sorry.
- and in the last series, when the doctor is meant to have been erased from history, she wanders past Amy's wedding, whereas in a world without the doctor she wouldn't have existed at all (no doctor, no canoodling in the Tardis)
She may well have still existed because shes their child - they may well have always got together. But agreed this is the old 'Grandad paradox' wrapped up in another form.
- She also seems to be able to influence the ageing process - can time lords choose to grow up (from toddler to woman) or go backwards, or indeed stay static (as Matt Smith presumably did over 200yrs)
River isn't a time lady, she is human plus time lord. i.e she has a 'time head'. Old wisdom on the Doctor was that the time lords were sterile and they they were woven on giant looms (see the Cartmel Master Plan from the McCoy era).