Your best bet is to discuss this with the Jockey Club. They need a clear trail of ownership. This is first of all on the back of her papers, but it is also secondarily recorded electronically on the Jockey Club Interactive Registry site. There is a whole thing there about tattoos, etc. It’s a process and you may need to trace back her ownership until you find the person who has the papers and find out why the papers never went forward with the mare. It could be that there was a payment dispute and this will add a few wrinkles.
You are better off shying away from this mare and finding another one for breeding who has her clear line of transfers, records, and papers intact. Buying a mare without papers means you are accepting the seller’s hearsay on who the lineage is unless you have already received verification from the Jockey Club that the tattoo is linked to a definitive XYZ mare sired by Y stallion and out of X mare whose damsire was YY. I always strongly recommend to people looking to breed to only engage with sellers/horses who have the complete paperwork intact. It can be, depending on circumstances, sometimes very difficult to get missing papers reissued and there is no guarantee the Jockey Club will willingly do so as they are not required to. The onus is on the current owner to submit an affidavit as to WHY the papers went missing in the first place, and you have to prove this to the Jockey Club’s complete satisfaction before they will even consider it. There is good reason for their hesitation and due diligence - too many horses have papers go missing and if they just handed out duplicates like candy without some stern and strict questions, some horses could be mis-papered meaning wrong papers to wrong horse, and the like. Their first and foremost priority is to protect their studbook.
Registration papers and/or registration passports need to be handled like gold. They are mishandled far too much in horse sport. They are key elements in the precise identification of the horse. The tattoos, branding and microchips are secondary.
So my recommendation is to pass on this mare because she has a dubious pedigree (not proven because there are no papers to prove it) and a dubious selling history (no list of prior owners because the papers are missing). Papers with the horse also prove that she was not stolen some time in the distant past, not necessarily accusing her current owner, but perhaps somewhere deeper in the past. No papers = no LEGAL proof of anything.