Feeling Guilty

Joey and I decided we wanted a baby when I was 21 and he was 22.  We tried for over a year before I became pregnant at 22.  I turned 23 while pregnant.  My pregnancy was hard.  I had morning sickness the whole time, gestational diabetes, premature water breaking, my feet swelled so much that I couldn't fit them in anything but sandals, and my job required close toed shoes so I endured months of cramming them in.  I barely slept, I never got that 'glow' people talked about, instead I was constantly told I looked like crap.  Don't get me wrong, it was worth the end....and everytime I felt her kick(and she was a kicker) it made it just a little more bearable.
 
However, even as we tried, we seriously talked about the possibility of this being our only child.  First off, it was so hard to conceive, second off, I just don't know if I want another child.  Motherhood is hard, rewarding, but hard.  And I'm constantly stressing that I'm going to mess her up, I don't want to mess up two kids!  And we don't want to have another baby unless we are financially sound enough, and that doesn't look like it's going to happen!  We decided that if we did have another baby we wanted to wait until Marlow was 4 or 5 to have it. 
 
First comes the constant flack from family and friends.  How it's cruel to make Marlow an only child.  How she's old enough now that if we want another I should already be pregnant.  How 4 or 5 years is too long and they will never be close.  My brother is 7 years older than I am, and he was one of my best friends, until he got married.  We hear about how it's really not 'that hard' raising a toddler and having an infant.
 
But recentley my little sister and I had a 'discussion' and I feel so guilty.  She has always wanted 4 or more kids.  She loved the idea of a big family.  She got pregnant with her son, Julian, while she was in an abusive relationship.  She left him and became a single parent.  Then she met Danny.  I know they are planning a future together, he told me last week that he wanted to propose to her on Christmas Eve in front of the family.  Julian is 18 months, and they have been trying to get pregnant with no luck so they went to the doctors.  Danny has low sperm mobility, and my sister has about 5 viable eggs.  The chances of them conceiving are slim...her good eggs could be wasted one right after the other, or it could take years to dispel them all.
 
We were talking about me having more kids and I told her that I was leaning towards no, but I wouldn't rule anything out yet.  And she started crying, telling me I was selfish and it was unfair that I would refuse to bring more wonderful little people into the world if I could.  She told me that I was taking a gift God gave me and wasting it(I'm an athiest, but I know enough of how believers feel to know that there was real passion in this statement).  She then brought up that her and Danny have talked about how, if in five or six years, they are still not pregnant, what options they would consider.  And so far surrogate mother was their favorite option.  Then she asked if I would ever consider doing it for them. 
 
I told her the truth.  I didn't know.  And she started crying harder and telling me that I was her sister, and she thought I loved her enough to just go ahead and agree to it.  But, that's a huge decision to agree too.  And sure, it may be a moot point as in years they may have another baby, but if I was to agree just to calm her down she wouldn't forget I agreed.  I don't know if I could carry a baby, birth a baby, give the baby up, and still see it on a regular basis.  I think that may tear me up.
 
In the long run, I feel selfish, and weak, and ungrateful.  She want's kids so bad and she may never have another, I doubt I want anymore and as far as I know, I could have more.  Yet I'm unwilling to help her out.  I know the thought pattern is sort of messed up, but it's how I feel.