Dog gone decisions

I'm not sure if I have talked about it here or not but Kevin and I have a dog.  We got her from a friend of Kevin's family about 5 years ago.  At the time we thought she was 4 but it turned out she was older.  The vet never knew exactly how old but we estimated she might have been more like 6.  Which means now she is 11.  Well on Wednesday we had to take our old girl to the vet.  Just her regular Old girl visit.  During the check up they told us that Annie is probably more like 13 now.  Not 11 and that Black Labs only live to about 13.  Just hearing this made me upset. 
We've had a lot of issues with Annie but I love her.  She is great with people, Great with Kids, but is AWFUL with other dogs.  She has really bad anxiety and hates to be left alone.  So when we first got her we got a dog walker to come in every day and walk her since.  Sometimes it helps her, other times she doesn't care and still creates a mess.  But, she's my mess and I love her anyways.  Well over the past few months we have noticed an decline in Annies health.  Her hearing is going, Her back legs dont work as well as they did even last month, and when she gets a little too comfortable she pee's a little.  This makes her very ashamed and she shows it.  So we took Annie to her appointment and let the vet know about all of what is going on.  500$ later the vet informed us that she didnt have anything MAJOR going on but her time is coming and if we want to start thinking about our options before she starts to be in pain, that we should. 
Well hormones kicked in and all of Wednesday I was a complete MESS!! I understand what the vet was trying to say but how can I even think about putting her to sleep if there is nothing MAJOR wrong with her.  That just seems mean to me.  Like I'm being selfish and giving up on my dog friend.  I mean, Annie sat by my side every day as I cried about Lydia.  She follows me now as my protector.  How can I think about putting her to sleep?? Then I think about Colin.  It takes a lot of work to care for an elderly dog.  Then an elderly dog with accidents? and not to mention the incontinents when she sleeps.  Do I really want to have that around when Colin starts to crawl? Will I be able to keep up with her health and take care of an infant? All of these things have weighed heavily on me this week.  It's a hard thing to feel like I'm trying to do right by her and still keep Colin's best interest in mind.  We obviously don't have to be in a rush to make a decision on this right now because she's not in any pain.  So Kevin and I agreed we wouldn't do anything until the new year unless Annie starts to go down hill.  But, it's still a really big decision.  It's so hard.  Now I truly understand why I never had pets growing up as a kid.  I cant imagine if Colin was here and older trying to make this decision to take away his pet.  I really don't think that I will ever want a dog again for a very long time. And here's a pic of our girl Annie....