Entering US within 4 months after previous visit?

[NPL]

Dear Forum Members,

I would highly appreciate your advice/feedback on the following situation:
My mom is currently in the US on a B1 visa. She arrived on November 1st 2009 and plans to go back home in 2,5 months.
I desperately need her to come to the US again in end of May 2010. The thing is, I am pregnant and expected to deliver May 30th. I have 2 small children already and this pregnancy is a quite difficult one. My mom's help is really a blessing for me now. But I need her to be here for the time of my delivery, to at least stay home with the kids while myself and my husband are in hospital, well, the usual stuff associated with arrival of the new baby.
This means that she would have to enter US approximately 4 months after her departure. Is that going to be a problem for an immigration officer? Is there a chance that they would not allow her to enter? Of course, she would have all the letters and documents verifying my condition on hand, but I just want to make sure that everything is going to be fine with her entrance.

Thank you so much for your responses.

 

[NPL]

1. Well, what is the date of her departure on her I-94?
or how many months was she given at the port of entry on Nov. 1st when she arrived?

2. Is this her first visit? (I mean Nov. 1st is her very first visit to the US?)

Answers to the above questions will determine her re-admission in May 2009

She was allowed to stay until April 26th 2010.
This is her 3rd visit to the US, fist one was 6 years ago, she stayed for 4 months; second was 1,5 years ago, she stayed for 2 months

 

[Triple Citizen]

There is always a possibility. Only US citizens have the right to enter the US.

Is that going to be a problem for an immigration officer? Is there a chance that they would not allow her to enter?