If you are in the US, the school can not refuse to do a learning disability evaluation if you request one in writing. The evaluation must be completed within a reasonable time.

Data from her response to a behavior plan can be included as part of the information the evaluation team considers, but a behavior plan is not a substitute for an evaluation. The rest of the process should be going ahead at the same time.

See this page from Wrightslaw.com for more information and resources.