I worked eight and twelve hour nightshifts during both my marriages, and when I was divorced raising three children. I didn't mind the nightshifts once I got use to them, but there were times when working nights did not benefit me family wise since I did not have any reliable sitters for my girls. You say that your parents have agreed to watch your child during the hours you are working at night, so I say go for it if those hours benefit you best.
The only problem is when your daughter is wide awake and full of energy during the day, you will be sleeping to prepare for another long nights work ahead of you. That may possibly present a problem for you.
If you work eight hour days as you have in times past, you will be able to spend more 'awake' time with your child. You'll be able to have supper with her, bathe her at night, read her a bedtime story, and put her to bed. Then, while she is sleeping, you are sleeping. This arrangement is MOST ideal for a parent with a child.
If you work 12 hour days, you'll not be home for her breakfast, lunch, or dinner. You will probably come home around 8 or 9 at night to put her in bed, or to kiss her goodnight after she's already been put to bed and is fast asleep. You'll be gone when she wakes up in the morning, so for the three 12 hour dayshifts you'd be working, you and your child would not have any time together at all. This might make her act out more due to not being able to spend more time with you during her active hours.
If you work 12 hour nights, you will be sleeping most of the day, so you may have one or two meals with her before taking off for work. Also, while you are trying to sleep during the day hours, she will be busy getting into things which may frustrate you if you have to keep trying to wake up to see to her needs. Nightshift tends to upset one's circadian rhythm. It's been proven to cause more heart attacks and other health problems in females, so that's another risk factor you may possibly have to face down the road.
If you work 8 hour nightshifts (11p to 7a), you will be able have one or two meals with your daughter, story time with her before bed, then be home to put her to bed at night. She will be asleep when you leave at night for work, and awake waiting for you when you get home in the morning.
Well, this is pretty much the truth of working the various shifts. Have you considered working 3 to 11 yet? That's not a bad shift for a parent who has a 4 year old child who would be in the care of her grandparents during the evening hours.
I've tried them all, so you just have to be flexible enough to change shifts as your family changes according to their personal needs as well as your own. I'm sure you'll do what is right by yourself and your child. You are very blessed to have parents willing to be there for your child whenever you work. That is something I never had. I hope this information proves helpful to you. :kiss