Hi there - I think it's very doable.
I'd be inclined at her age to let her hold the cup herself (just put small amounts in at a time if it's spillable).
Give her what you've got! You're not going to have tons of EBM, I suspect, so I'd aim for around 4-6 oz at a time. At that age, my lo's would take about 5 or 6 of EBM from a sippy (DD1 never had bottles).
Pump first thing in the morning after her morning feed. You can also try pumping after her last feed of the evening (though you might not get much to start). If you really want to do extra, you can pump about an hour after her daytime feeds too - if you do it at the same time each day, you might start to notice your output increase.
As for how long - it really depends on your supply.
If you want to avoid cow's milk, I'd go with whatever EBM you can produce, water, and make sure her diet is varied enough - some kids never drink cow's milk.
No way to know if you can return to BF after, but for only 4 days, I'd say the chances are pretty good. You might have to use some extra encouragement at first, but I'd be hopeful!
Good luck!