"The only asset in the partnership is the campground land"

Yes; owned by the Partnership; not Inherited by this spouse.

"Should there have been a appraisal of the partnership at the date of death to determine FMV of the 50% interest in the partnership?, which I don't believe there was, or since the only asset in the partnership is this land, can I use 50% of the FMV at death?"

What about liabilities? Basis from years of operation? Money in the bank is also an Asset.

"If I can't use the FMV of the RE,"

The RE is not what was inherited.

"and no appraisal was completed for the partnership, do I have any options for a stepped up basis?"

Did you read the info at that link?