The only time I hear from my daughter or son in law is when they want us to babysit their 8 yr old so they can get away. If we say no, then I don't hear from her for weeks and I start feeling guilty about what did I do that made her mad. It's been this way for years and I am very frustrated as she is not the type of woman that is open unless it is her problem that she needs to talk about. I want to call her but then if I do, it opens the door for us babysitting and we are retired and my husband gets mad at me for breaking down.
What do you recommend I do, call her or ignore her and keeping peace with hubby?

How far apart do you live? Do you see them at times not when sitting, like for dinner at your place or a cookout or to eat at a restaurant?

We live about 20 miles apart but traffic is really bad. We rarely meet for meals or events unless it is a birthday or Christmas. My 39 year old daughter feels that if I say anything to her regarding our relationship, she'll say it's all in my head and that I need to get a life. I am always giving and helping them when they ask, but it's never reciprocated or appreciated. I love her and my grand daughter but am constantly scared to speak up to her knowing she'll put blame me but won't tell me what upset her. Ugh!! So therefore, I'm in a constant state of anxiety, depression, and stress.

Many people would write in here or complain in other venues that they never get to see and interact with their grandchildren and it sounds like you have very little opportunity to do that, if you see your children so infrequently.
Are there some other factors involved here, possibly?

"if I say anything to her regarding our relationship, she'll say it's all in my head and that I need to get a life"

Tell me more about this. What about your relationship? What's all in your head, according to her?

Do you communicate with your granddaughter via snail mail or email or phone? Send funny cards or drawings or kid riddles or jokes? What I would do is take a sheet of printer paper, neatly print a kid riddle on one side, add a few silly drawings that fit with the riddle, and put the answer in a small sealed envelope labeled ANSWER, and mail all that to your granddaughter. The public library has lots of joke and riddle books for kids or there are similar websites, if you need ideas. Or even print several sheets, each with a riddle and stick figures or simple drawings on it, number each sheet, and then number the answer envelopes that match each riddle.

Or something like that.