Louisa was a very money-minded lady and she did not wish to perform any extra work apart from what she had been paid for. When both Louisa and Mrs. Packletide were seated on the platform, waiting for the tiger to arrive, then Louisa made this remark. She simply wanted to highlight that there was some danger to her life from the tiger.

I am asking what the danger was.

Louisa Mebbin was a crooked lady.She remarked that they were in some danger because she thought that the approaching tiger could cause any sort of harm to her in the dark.

In the book it's written that Mebbin was not at all afraid of the beast

Otherwise I think Louisa makes this remark to draw Mrs Packletide's attention towards the extremely old and senile condition of the tiger that they were about to shoot. She wanted Mrs Packletide not to spend a thousand rupees for that old tiger. She actually wanted her to do some bargaining with the village head-man regarding the reducing the price. Louisa had protective elder-sister attitude towards money. She was extremely greedy and selfish lady

Also Louisa Mebbin did not want to work more than that she was expected to as per her payment. So she told this.