Supsherpa, been there a few times with couple of shoulder reconstructions, bicycle and motorcycle misadventures mainly. Worst was slow-speed over-the bonnet of a car turning in front of me resulting in ruptured supraspinatus and infraspinatus tendons, ruptured bicep and glenoidal labrum tear. Insurance covered me for significant rehab after the op which had me doing very little else physically other rehab for 3-6 months. I was doing triathlons at the time so that buggered me around a bit.
Of relevance to you and your question, although our injuries may differ a bit, I was told I would never have more than about 130 degree vertical arm movement and never be able to lift more than 15kg LHS. Well after relentless rehab, a year officially but well beyond that personally, I have almost vertical rotation and probably 85-90% strength back. I am weaker on that side but it barely compromises anything I do (apart from drunken wrestling - don't do it!).
One thing that made a significant difference for me was an intensive weight rehab program I did for three months 3-4 times a week both upper and lower body in tandem with good physio advice and top-shelf masseur for about year (yes thank God for insurance). Invaluable that strength conditioning bit by bit bringing your body back. Also did lots of stretching and own rehab. Perseverance pays.
Answer to pushing too hard is your body will let you know, but go softly softly to start off with. That's where lots of strength conditioning comes in, physically supporting that most complex joint in your body. You also need to be ever aware of proper technique (paddling, swimming, even running), tucking that scapular in to avoid impingement. Bone, ligaments, tendons, cartilage - everything that is your shoulder capsule - takes good time to heal. You'll come back no worries though!
Good luck, but more good management and she'll be apples!