Some Christians are so myopic with the idea of girls putting on trousers, they seem always to refer to the Biblical passage of Deuteronomy 22:5 which says that a man should not put on a woman's cloth and vice versa.
Now let us look at the meaning of that passage:

1. To the original people(The Israelites) whom this law was given from the Lord of Host, there is nothing like trouser in their cultural and native attire/dressing. Bringing it to our generation on the basis of trousers, we are giving a whole bunch of wrong interpretation to it.

2. In the heart of every human being, there is a sense of descency which tends to condemn everything that is bad and commend everything that is good from the very first sight. So does it happen with our respective dressings which most at times seem to be immoral though it is not a trouser (I mean those who wear mini skirts, push-up bras, transparent cloths, and lakra, lighted and nylon material cloths). All of them are indecent though they are not trousers.

3. The main and ultimate purpose of "cloth" is to cover up our bodies. In Christian morality, it could be added (in a responsible manner). Therefore, any good material that you used to cover up your body "in a responsible manner" is never indecent.

4. According to my Catholic Bible of African publication (AFRICAN BIBLE) which gives a brief explanation of Bible passages with regard to African cultures, it condemns transvestism with reference to deut 22:5 and not putting on of trouser by girls. Transvestism refers to a man putting on a woman's cloth "for sexual purposes". Therefore, the law was pronounced for those who seek attraction from same sex (gays).

5. In our original African culture, not even men wear trousers but it was civilization that brought about the idea. But now, some people term it "a sin" when they see women put it on because our mentality tells us that it is a sin but it is not a sin in the reality.

6. Women wear trousers to avoid the risk of rapes and to enhance easy movement of the body especially in times of danger.

6. If we call it a sin in itself, then, we are indirectly condemning all(females) who put it on as enemies of God and would be condemned to hell if they do not stop it. Then all whites will be in trouble because they put it on everyday of their lives

By my defence of wearing trousers by women, I do not in anyway affirm that it is advisable to allow them to come with it to church or holy services unless it could be monitored or regulated. Because as Africans, we copy from the whites and do worse than they did. If the freedom is given to Africans Christians, it will give not even room but hall for abuses.

With these facts of mine, I wish convince our narrow minded Christians that wearing trouser responsibly by girls is never a sin.

Same law applicable to the male counterpart wearing ear ring, and plaiting

whether we like it or not men and women have different ways of covering their unclothedness.. @OP I don't know your faith, but if you're a Christian, then the bible is clear about this subject in Deuteronomy 22:5. so don't try to twist facts to align with your argument.. Trousers remain and will always remain a male thing no matter how you try to twist it. Bros, how then you don't wear skirt and blouse to office? The reason is simple, because they are meant for our women folks. Now, this how it is in the bible, and if we call ourselves Christians, trousers remain a no go area for women, that is what makes it a SIN.
Now, one would argue that women of those days were not faced with the challenges of rape and molestation we have in our present day and that's the reason they were able to comply to some reasonable extent, to those biblical laws, but we must remember that laws are laws and they're meant to be complied with. We now live in a more liberal world with other faiths in it and also those who don't believe in any faith at all, that's why there's need for laws that will accommodate different people no matter their faith and believe. These have given birth to women libration movements across the world, where women want to be equal to their men folkz. in order to do this, they need to think like men, talk like men and dress like men. What we call female trouser today, is just an amendment to the normal trouser, to suit female shape and size.
Personally, I don't have problem with my lady putting on trousers, but it has to be modest and decent, but that doesn't make it acceptable in Christian Dom..