But isn't the battleship HMS Lion under construction at Newcastle upon Tyne when the war begins? Even assuming that anything of the battlecruiser HMS Lion was left to reassemble (she was sold for scrap in 1924!), why would one settle for resuscitating that hull, when she could be provided a bigger, brand-spanking new ship?
Unless that is what you mean by rebuilding warships that were scrapped. If so, then the only thing standing in the way of Vickers Amstrongs turning out a new receptacle for her would be labour and materials.
The very same things that stood in the way historically. If things had turned out differently and there had been consistent available resources to finish her? Who's to say?
I do think that the Captains of Belles have a war to fight though and while it may be Neutral, the INPF isn't a country. Shipbuilding from scratch should probably remain in the hands of the various countries, if for no other reason than even with a freshly commissioned ship and crew (and a handful of souvenirs from her battlecruiser days) , there is no certainty the Belle of HMS Lion would awaken. (And the Royal Navy is gonna need every ship it can beg, borrow or build).