I enquired about buying my house. It depends on what contract she's on. most housing association houses that are a 2 bed are on a assured tenency so she'd be fine with that. But it also depends on what house is classed as. I couldn't buy my house as I am on a fixed term assured tenency because it's a 4 bed, every 7 years I'll get a review of my housing needs. They'd never kick me out as such once my housing needs are less, but they'd chat to me about downsizing. It also depends what area the house is in.
Please understand that council houses (council do not Build anymore, they simply have old stock from before housing association took over) and housing associations are completely different. They're extremely iffy with right to buy because of what happened last time. Everyone bought their house so cheap, that those who needed housing, there were simply none left as council didn't build anymore.