From someone who's been in exactly the same situation but from the opposite side please let me reassure you firstly that this will pass.
I suffered (and friends who have also returned from maternity leave agree) from what I can only describe as 'baby brain' for the first 12 months after we had our child.
'Baby brain' as we refer to it is, is generally caused by having spent the last 6/9 months where the majority of your human contact is spent with someone who makes only gurgle noises and weird faces. The fact that your mind is literally still reeling from the fact that you actually made a tiny little person and that the blob that they start out as quickly turns into an actual tiny person with moods and mannerisms all combine to make them literally your entire world.
It follows therefore that you genuinely can't comprehend the possibility that another person won't find your baby's antics as amazing and hysterical as you do.
Odds are that she has absolutely no idea that she's a) prattling on incessantly and b) that you really don't care.
There's potentially other factors at play, if it's a first child then there's possibly a bit of separation anxiety and guilt on her part that she's at work and might miss some of the major milestones like first word, crawling etc. Talking excessively about baby's antics may be her way of reassuring herself that she's not essentially neglecting her child by coming back to work.
I'm honestly not trying to justify it, once this period had passed for me I found it just as annoying when friends went through it so I understand where you're coming from. However I do remember what it was like, so tend to grin and bear it.
If waiting it out (honestly this phenomena should pass), isn't an option then you can gently and tactfully try to explain that you have pressing work/deadlines etc.
If it's possible, having things like a couple of photos on her desk (maybe as a collective gift from the office) can go a way to giving her the 'constant contact' she's craving.
Lastly, once this period of time passes you may find that it's even beneficial. The days where big business client relationships were maintained on the golf course or in members only clubs are fast waning, partially as a result of increased numbers of women as CEO's and in senior management positions.
I've traded some pretty funny (to us at least) child related anecdotes with clients (both male and female) before. This has established some common ground with them and makes both sides view each other as human. To the point where meetings can start with a quick 'how are the kids?'. This human side to the relationship can have its benefits when it comes to retaining client loyalty etc.