Family Tree DNA uses buccal swabs, which collect skin cells from the inside of your cheek. As a result, it is very unlikely that the FTDNA test will be influenced by a blood transfusion.

Is the Native American (NA) heritage in her direct Y-DNA line (her father’s father’s father’s father etc) or her direct mtDNA line (her mother’s mother’s mother’s mother etc)? If so, then any Y-DNA or mtDNA test would answer whether or not there is NA ancestry in those two lines.

For all other lines (her father’s mother’s line, her mother’s father’s line, etc), then the testing for NA ancestry isn’t as exact. Some companies offer autosomal testing which attempts to estimate the percentage of NA, European, African, and Asian ancestry based on markers throughout the genome. However, these numbers are VERY rough estimates based on a few thousand markers out of 3 billion bases in the human genome. I’ve had it done and it is interesting, but I wouldn’t rely on it alone.

As always, genetic genealogy is at it’s best when it’s combined with traditional genealogical research!