Not sure if this is actually on sale, but assuming so based on the price for the individual books.
Amazon only.
Ruby Lionsdrake
Mandrake Company (The Complete Series: Books 1-7): A Science Fiction Romance Bundle 99¢
Amazon
FWIW, I read
The Pirate Captain’s Daughter a few years ago as it was in a box set I bought at All Romance eBooks (remember them

?) back in 2015. Also, the bonus short story was in one of the Pets in Space anthologies. I enjoyed both and have also enjoyed the books I've read that she's written under her real name, Lindsay Buroker. (I have a ton more of her Lindsay Buroker series in my TBR mountain).
The full-length books are usually $3.99 each plus book one and
The Pirate Captain's Daughter are $2.99 each, so 99¢ was a good deal and got me to
break temporarily suspend 
my 'I don't buy Amazon-exclusive books' rule. The series used to be wide, and I'd been waiting to see if she will ever put it back into additional stores, but for 99¢ I admit I totally caved

Also,
The Pirate's Captain Daughter used to be listed as a novella on her website back when she had one for her penname (so #5.5). But since it's been reclassified as a short novel for the box set I went ahead and changed the number in Calibre to match (so now it is #6.)