Is it obligatory to purify oneself standing or sitting when feeling toilet water splash back while relieving oneself on a Western-style toilet?

If a woman is certain that some impure water has splattered onto her garment while she is sitting, she is not required to stand up to purify it. Rather, it is sufficient for her to pour water over the impure spot. It is permissible to use a bidet for this purpose. What is required is to pour water over the impurity until it is highly probable that it has been removed.