In reply to drink_more_tea:
I'm guessing its stopped exploding? or has it?I Just read this,
http://www.markhorrell.com/blog/2017/is-cotopaxi-now-safe-to-climb/
Yes you know the answer to this! All you need to do is persuade your sister in law!
No disrespect to your Sister in law intended, but it always amazes me where these clients come from and how many there are, not to mention some company's willing to take their money (or worse) simply because of their ignorance! Now that's of my chest, back to the point!
Don't know Cotopaxi it has to be said, but in general as a reasonably fit individual, who regularly leads people up to 5,600m I normally work on 1 day for every 1000m gained + rest day + summit. So from sea level to 4800m = 5 days, then rest(ish) day, then summit, so 7-8 days. If she's already at 2800m for a while and happy, you could knock 2-3 days off this. The lack of skills and experience is a different matter and it would feel very intimidating to the uninitiated. Having said that with a good guide and small ratios its not to much of an issue skills wise. I'm sure there's many other trekking peaks in Ecuador that may be more suitable for a beginner.