My son had bloods for thyroid recently, he's 2.5.
They took it from the inside of his elbow.. I won't lie to you. It was horrendous but my son had no understanding and is extremely shy, he won't stand on the scales to be weighed or have his height done so I knew it would be bad.
They offer you a numbing cream which you put on and wait 30 mins. It goes under one of those big clear plasters, I declined the cream as he wouldn't sit with a plaster on and that alone distresses him. So I decided to just go with it, I had to hold him in a bear hug with his arm round my back, another nurse pinned his arm back and they put in the needle and filled several vials of blood. Only one needle in the skin though.
There was a play specialist who attempted to distract him, but he was way to distressed, imagine it works well for some kids though.
We had his bloods done at 11am. At 7.30pm I got a call asking me to go straight to a&e as there was an issue with his potassium levels, a quick google gave some awful reasons for this alongside the need to go in immediately I thought the worst! 2 more lots of bloods in a&e as equally distressing as the first but I didn't find out until the last test that it's very common for children to give false high potassium readings due to the trauma of taking the blood. In a panicked state the blood releases potassium which causes the high readings, 3rd test was normal and so there was nothing wrong. Really wish I'd know that before hand as it could if saved me so much upset thinking something was wrong.
Maybe do some role play before hand? Get something thin but obviously not sharp and show her how it's done, and say this is how the doctor will do it, let her do it to you etc. We took his favourite toy and the doctor examined the toy before she done him and that really helped him but didn't help with the bloods at all.
If your child will have the numbing cream and will interact with the play specialist then I imagine it's quite simple and easy.
I know it isn't a positive example, but just wanted you to feel prepared for the worse case. As soon as it was done he had a big hug and kiss, chocolate bar and a new sticker book and skipped out the hospital happily.