There are many legends that concern the Shawnee. Their early religious traditions included a female supreme deity, the grandmother. So women always held a special place in Shawnee culture. Most of these legends and myths, as told today, are amalgamations of stories told a century ago, those stories told a century ago were amalgamations of stories 2 centuries ago...and so on and so forth. Once inter-tribal culture in the Shawnee began to flourish, along with contact with the French, the Shawnee changed their stories..and a lot of the religious stories took on a Christian flavor...which happened in most Native cultures. I believe I have heard, vaguely, of the story you tell.. It may be derived from the Mica Giant story in the 19th century, a 9 foot 8 inch tall skeleton found in Indiana who wore huge pieces of mica as a necklace, of course the bones were lost...go figure...so there is no proof.. The graves lined with Mica derived from the Hopewell Tradition, also called the Hopewell Culture, which flourished 1000 years before the separation between the Fort Ancient and Shawnee cultures, the Shawnee of course were actually the Fort Ancients...
The part of the tradition that is to be scared of is the location of where certain burial grounds exist. I know from experience the power of Native American burials. I have recovered, from the authorities of course, Native remains in the past for reburial and I still have "something" in my home that came with the remains.. God pretty much let me know that it's harmless and to basically leave it alone, so it appears I have a permanent house guest. I help folks get rid of things in their homes, and I can tell you if you mess with the spirit world, Christian or not, and you are not prepared to take on what's waiting for you, it will result in a big butt whipping.
You say Christians shouldn't fear something like this? Remember this exchange between our Lord Christ and his Disciples:
Matthew 17
15. Lord, have mercy on my son: for he is lunatick, and sore vexed: for ofttimes he falleth into the fire, and oft into the water.
16. And I brought him to thy disciples, and they could not cure him.
17. Then Jesus answered and said, O faithless and perverse generation, how long shall I be with you? how long shall I suffer you? bring him hither to me.
18. And Jesus rebuked the devil; and he departed out of him: and the child was cured from that very hour.
19. Then came the disciples to Jesus apart, and said, Why could not we cast him out?
20. And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you.
21. Howbeit this kind goeth not out but by prayer and fasting.
Remember this and take to heart, don't mess with certain things, especially burial grounds or it will result in your destruction unless you are powerful enough within the Kingdom to take it on... Even Jesus' disciples were powerless against certain entities.
I have had enough experience with the Pow Wow circuit story tellers to ignore around 95% of the stories told by other Natives. The real stories, and deep dark legends, that are held in extreme secrecy will never be revealed outside of a certain circle and these stories, which I have heard pieces of concerning this area has nothing to do with giants and female leaders of the old times. I will tell you this much; people on this forum have posted certain carvings that pertain to these legends and I can guarantee you no one, aside from one person I know who visits this forum, has a clue what these carvings indicate..and I will never tell... So the fear likely concerns a burial place that if disturbed will open the gates of hell on the person who disturbs it...and that happens from time to time...