I've done meditations to meet my spirit guide but have had a block every time. I went to a local shaman who said it was female, but he could only pinpoint a name like Mara and that she had a green necklace of some sort around her neck. He couldn't give me any other answers, so I'm not sure if he could really tell. Does any one have any tips?

Do some digging on Google. Maybe it will have some death record results for a mara. But I recommend if you really want to get through to this spirit you should take advantage of the information you have. The fact that she has a green necklace was one of the only things the shaman could pick up means it must be very important. Next time you try to meet her try burning a green candle or wearing some kind of green.
Hi Alice! I do a lot of spirit work and whenever i’m reading someone and encounter a block i go about it like solving a puzzle. Breaking down the clues you know, try to visualize a woman with a green necklace while meditating and see what appears. Names are powerful so focus intent into something like “Come to Me Mara”
Candles as well as mirrors are great for focusing energy so perhaps set up a mirror and candle in front of it and just let your mind wander.
Hope this helps! Feel free to talk to me whenever