I’m baffled by the idea this is discrimination. I can’t see how it is, even with the update.
OP asked for what essentially amounts to a demotion- less responsibility, lower workload and reduced hours. Her employers agreed to this and created a role did her- that reflected her request but (entirely reasonably) attracts a reduced hourly rate of pay due to the reduced responsibility and workload. It sounds as though they may have verbally offered OP’s job to the person who provided her maternity cover, on the basis that OP had indicated she did not want this job, but wanted the role they have created for her (although OP does not know exactly what form this offer took- it could have been a verbal offer or “ if x were to leave, would you be interested in staying on?”). OP then said she wanted the same rate of pay for the new role, which is clearly unreasonable- at which point they said she could go back to her old job if she wanted.
Whether they have verbally offered it to someone else does not impact on OP- unless they followed through and refused to allow op to return to her job. I’d be surprised if she could claim discrimination if she is able to return to her old role (or it’s equivalent), regardless of whether someone else was offered it verbally or not. Depending on what was said to the person who is her maternity cover, they may have a case or be entitled to compensation (perhaps not- it may be just notice pay)- but that has absolutely nothing to do with OP’s case. The only thing that matters is whether op could return to her old role, or an equivalent, on the same T&c’s. Her employer has categorically stated she can return to her old job, so no discrimination case, surely?
At some point in this process a restructuring of the business (or at least the part of the business OP is employed in) and her original role has been tweaked and renamed (effective as of April)- but it is still the equivalent one to the job she was doing prior to maternity. She has been told she can return to this job, which is equivalent to her current job.
What she can’t do is the new role but retain her old T&C’s. She has to choose old role (i.e. the equivalent in the new structure) and the higher salary that role attracts; or she can decide to take the offer of the new role which is what she asked for, but with the lower salary which reflects the altered responsibility and workload.
It’s not discrimination and it seems to me that her employers have tried to accommodate OP’s requests, within reason. It’s very foolish to assume that you can decide to step down in terms of responsibility and workload (albeit for understandable reasons) but keep the salary the same (or even the same pro-rata) on the basis you are returning from maternity leave. You are entitled to return from maternity leave to an equivalent role with similar terms and conditions, but you can’t decide/request to change your job to an entirely different one and keep your salary on the basis you are returning from mat leave.
I think it’s pretty poor behaviour and does not show you in a good light OP. I’d be quite frustrated if I was your employer. You do need to decide which role you want and let them know so they know what they are doing, going forward.