No - they cannot make an employee redundant during maternity leave, but they can once an employee comes back. They can even issue notice of redundancy before or during mat leave but this only takes effect after the maternity leave is over.
However, the employer has to apply fair criteria. The fact that the team worked in the absence of one of the workers does not mean that that particular worker is redundant. They can apply criteria of performance, seniority and a whole load of other things to determine redundancies. Most teams manage while someone is on mat leave for a few months. Your scenario would mean that taking mat leave makes someone a more suitable target for redundancy, which is discriminatory too.