We booked our rescue dog in to be speyed last week, luckily we knew the date of her last season. Took her in, vet checked her over and told us she was lactating! He said she was having a phantom pregnancy. Not expected! There were no signs that I know of, she was her usual self. She's about 8 yrs old and we have no other history from before last November. She was put on Galastop for a week and we went back on Friday to check. No milk but some serous fluid. The vet didnt really think (less than 10% chance) that more Galastop would help stop the fluid, so she's now due to go in next tuesday for her spey.
According to the vet there's a small risk of her being speyed at this time and getting 'stuck' (non scientific term!) hormonally at this point in her cycle. But if we wait she may come into season again and we would need to wait another 3 months after. She's not getting any younger and is already at risk as she is a giant breed.
Anyone have experience of this please?

She was checked today, prior to spey and she still has blood and serous fluid coming from her teets. The vet decided to put her on a weeks antibiotics just in case  there is any underlying infection, and delay her spey. Poor girl, second time she's gone without breakfast for nothing!

do you have to have her speyed as part of the requirements from the rescue centre ?

Yes and I personally want her speyed anyway because of the increased risk of pyometra.