Yes, ds1 has low muscle tone and hypermobility and at 15 months still couldn't roll over or get himself to sitting. He is now 7 years old and takes full advantage of his photographic memory, phenomenal imagination, unusual abilities at mental arithmetic, reading and writing to make up for his need to rote learn physical skills and his comparatively poor visual manipulative skills. He was late talking, as a result of low tone in his mouth, but by 3 was clear enough to be understood and well within normal bounds.
I would thoroughly recommend physiotherapy - not just as a one-off until your dd is walking, but again when she is a bit older, to increase her strength just to be able to enjoy playground games, more, and to make physical tasks easier, particularly if it turns out she does have difficulty with working out physical skills for herself (it's hardly going to be easy to work things out for yourself if your body doesn't, in any event, have the oomph to carry a task through properly, so low tone left untreated will merely serve to exacerbate the symptoms of poor motor planning, otherwise). The physio taught my ds1 how to roll, get to sitting, pull to stand, crawl, climb stairs and walk... and in the last year, has provided very useful exercises to increase his muscle strength around his hips, knees, shoulders and core. Other things that have worked with ds1 have been: spending hours at soft play areas and in playgrounds shoving his bottom up and down things and physically manipulating his body to help him learn how to, eg, climb, skip, hop, jump, pedal a trike or bike, walk along a beam; subsequently, swimming lessons (individual worked best); keeping him active so as to build up muscle strength; painstakingly teaching him anything physical, including dressing skills; not letting him give up on physical things before he'd gained some degree of mastery over them; piano lessons (these have been hugely successful - at last, we found something he enjoyed doing with his hands); and some retained reflex therapy.... Ironically, he never needed help learning to write - I guess the formation of letters can be pretty quickly rote-learned, and as I say, his memory is unusually good, fortunately, since it takes the place of instinct... Basically, as he gets older, things have got easier, because he has acquired more and more physical skills that help him towards independence and once he can do something, he can do it quite well. At the beginning, since most of what most babies seem to learn relates to movement, it seemed like a huge task to help him, but it doesn't seem too bad at all any more.
One big thing I did learn was that worrying about whether my ds1 was the way he was because of his hospital treatment, or events during my pregnancy, was the biggest waste of emotional energy in my entire life. He was and is the way he is, and panicking about whether things could have been different if this, that, or the other had been done differently, was a huge hindrance to getting on with dealing calmly with the adorable little boy I had. If I had a child with severe, lifelong physical or cognitive problems that would be one thing, but I don't, I just have a totally adorable, eccentric, extremely clever little boy who will grow up to lead an independent life, even if it will require a bit more input from me to help him reach physical independence (and gain a modicum of common sense!), so the initial quest to find out why was a bit of an emotional drain of a waste of time in the end and did not result in any answers, just lots of prodding, poking and upsetting situations for ds. And it is rather lovely to be able to get all excited about what for most children would be irrelevant achievements, but for my ds1 are another example of huge strides towards being able to do everything that other children of his age can do (plus a lot of things that other children far older than him still cannot do).