If Windows 8 isn't going to run properly (not sure she would use the apps to be honest) then I'll probably stick with Windows 7. Thing is it was fine when she first had it and since then it has been upgraded to 2GB RAM so a fresh install of windows should improve it. I know over time it can slow down and she does also install some crap on it (but I'm slowly teaching her not to just click on install when prompted) but the fact is I can just provide it to her and leave her be. If I put something on it which doesn't look like Windows regardless of whether it is better or not is probably going to end with her telling me that she doesn't like it and wants Windows back on it.
If we had the time I think I'd go along with putting a Linux distro on it, but with a 1 year old which takes up lots of home time, she hasn't got the time or patience (nor me) to be learning a different platform. I might end up sticking with Windows 7 then if there is improvement with 8, I just thought with my experience of 8 it seemed a little quicker than 7 on the same hardware.
As others have said I haven't got the money for a new laptop and a tablet isn't a viable option as she may do more work on it as she increases her hours. Hence the thought of an SSD to improve performance & lifespan but it I'm not sure she would notice any improvement for web based activities.
If you set chrome as her default browser and install the adblock plus extension it might stop some of the crap. You could also turn off some services (windows search) and do some other tweaks to help it run better.
I've upgraded my aspire one with both an ssd and ram. It makes it a much more usable machine - even if it is only a few seconds faster. I've also put windows 8 on it. It works well apart from the metro apps. This wouldn't be a problem apart from the app store not working. The 8.1 update is only available on the app store - at least as far as I can tell. I would probably stick with windows 7 on netbooks because of this.
If it keeps it out of the bin for a couple of years its probably worth it.
Chromium OS made our old netbooks very usable.