Who is the selfish one--my mom or me? (LONG)

m+j

I need honest answers.  I've asked friends and they've shared their thoughts, but I figure they are probably biased in my favor.  

I found out I was pregnant with baby #2 in December after our 2nd month of trying.  The first time it took almost a year to get pregnant.  A few weeks BEFORE I found out about baby #2, my mom booked an Alaskan cruise with her friends for late August.  If the baby arrives as scheduled, she will be in Alaska when baby is born.  My mother is retired and travels often. This will be her second Alaskan cruise with her girl friends in 3 years and probably her 3rd trip with them this year.  She has full insurance on the trip, so she can cancel at any time and lose little to no money.  My first son was two weeks early.  If this baby is early, she will be around for the actual birth but not long after.

A little background:  My father passed away several years ago and my mother moved to my hometown.  The rest of my family (inlaws and cousins) live a 5 hour plane ride away with the exception of my sister, who is a 2 hour plan ride away.  This is the second grandbaby for my mom, the first being my son.  I do have many close friends who live nearby, including a nice but overbearing neighbor who has offered her full support and plans to help in any way needed. 

Yesterday my mom and I had a little spat because I told her my MIL had offered to come to town while my mom was in Alaska and I thought she should stay at my mom's empty house since we won't have the room.  She basically said no and took offense to the fact that I was telling her MIL would stay there instead of asking which I dispute, but I honestly can't remember if I did just tell her how it was going to be because I was angry.  That's when I told my mom I thought she was extremely selfish for going to Alaska when her daughter is due since (a) she should be there for the birth of her first granddaughter (second grandbaby), and (b) I would really like her help after baby is born and she will likely be gone.  My mom disagreed and said "the trip was booked before you became pregnant."

My question is--am I expecting too much?  This is the second baby and she was there for the first.  Is it really a big deal if she goes on the trip as scheduled?  Or is she being selfish for going?   DH said it shouldn't matter--if she doesn't want to be there, we really don't want her there anyway.   Thoughts?