The simple answer is that you elect a person to parliament who happens to be a member of a particular party.
That election is not dependant on them being a member of that or any party.
They could change party and not need to be re-elected - Winston Churchill did! - Twice!!
It is a separate matter to expell members from the house of commons and although they have that power it's very rarely used - 3 times in 100 years
http://www.election.demon.co.uk/expulsions.html
This was generally cases of deliberate fraud.
This case is very different:
1/ You're jumping the gun she's only being investigated at the moment
2/ I don't think she's being accused of a criminal offence at this stage
3/ The party whip was withdrawn not because of this but because she appeared in a TV show.
A power of recall would not be practical - you'd have to have a by-election to determine whether the constituancy wanted it and in that case you might as well just have a full by-election.